U.S. Pat. No. 3,929,316 dated Dec. 30, 1975 and entitled "Non-Floating Seat Structure for Expanding Gate Valves" shows an expanded gate valve having a valve body with annular recesses in which annular seats are pressed. An annular seal is positioned within facing aligned grooves in the back face of the seat rings and the opposed recess walls with the seal being of a cross-sectional area before insertion slightly larger than the cross-sectional area of the two opposed grooves thereby compressing the seals when the seals are pressed into position. This arrangement provides a fluid-tight barrier to fluid pressure tending to seep behind the seats and float or move the seats toward the gate. The arrangement shown in the above mentioned patent has functioned in a satisfactory manner but it is sometimes difficult and costly to machine the annular grooves in the valve body as limited space particularly in small diameter valves is provided for the machining of the annular grooves in the recess walls from the valve chamber.